Certain multiple-wavelength methods for interferometrically determining absolute distances between two objects movable relative to each other are conventional. In this context, one or more beat phases, which allow an unequivocal, absolute position determination over a larger distance range, are determined from the subtraction of interference phases of different wavelengths. In this instance, corresponding devices may also be configured in a cascaded manner, and starting from a plurality of different wavelengths, the generation of a plurality of beat phases may be provided. Regarding such devices, reference is made, for example, to U.S. Pat. No. 6,496,266, which describes a system operable using three different wavelengths, a plurality of beat phases and/or synthetic wavelengths being derived from the three wavelengths, and from this, information regarding absolute position being generated.
In the system described in U.S. Pat. No. 6,496,266, a total of three laser light sources in the form of stabilized He—Ne lasers are provided for generating the required plurality of wavelengths, which constitutes a considerable expenditure for equipment. In addition, a complex calibration of the plurality of light sources is necessary, in order to ensure that the emitted beams of light of all of the light sources traverse the identical paths in the measuring and reference arm of the interferometer. Furthermore, the three separate laser light sources require control of each individual light source, in order to ensure that the wavelengths of the individual lasers are stable over time and have a specific value.